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Bring Back 1962-63

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  1. Bring Back 1962-63

    Teleconnections: A More Technical Discussion

    LOOKING GREAT FOR EXTENDED COLD SPELL IN EUROPE AND EAST CONUS FROM XMAS ONWARDS At last, the AAM, torque and GWO charts have all just updated to Dec 9th and they are almost entirely in line with Tams' @Tamara and Tom's @Isotherm predictions and very good news for those hunting the main cold spell starting around or just after Christmas (I think)! Total GLAAM having fallen back is on the rise again. Following the huge fall in the relative GLAAM tendency anomaly it's bouncing back equally strongly exactly as they predicted. FT rose and has gone +ve albeit briefly. The rising FT (from its low point) has led Global MT up (with the usual time lag) and that's another huge spring back and leading NAMT and EAMT upwards. The GWO did not go -ve while it has moved from phase 8 and has pushed through the COD and is re-emerging in phase 5, exactly as Tams predicted. It's set to rise at increased amplitude through phases 5 and 6. I've run out of time (incredibly busy this week) to say any more but with the MJO also playing ball (entering a higher amp run through phases 5/6/7) and the signs of a significant strat warming (if not a major SSW) make me feel really bullish about a significant cold spell - probably in Europe/UK and the eastern CONUS. I'll leave it up to the rest of you to scrutinise the finer detail. I wonder how quickly the models will "fully" factor this in? David
  2. Bring Back 1962-63

    Teleconnections: A More Technical Discussion

    Short AAM/FT/MT Update Alistair @Catacol - I'll update what Zac @Snowy Hibbo and I were referring to yesterday with the latest available charts. It's early so they are showing the December 1st position but there have already been several of the "anticipated" changes that I mentioned yesterday. I'll show the 3 charts with short comments below each one and do a little summary at the end: I'll start with the relative GLAAM tendency anomalies (I'll shorten that to RGTA for the rest of this post) from Nov 14th/15th when it had been falling for about a week (albeit remaining slightly +ve). Then it rose slightly for 5/6 days until Nov 20th before falling for 10/11 days until Nov 30th/Dec 1st. Then, it is expected to start rising this week and there is a hint that is now underway (from Dec 1st). Given how low it fell, the bounce back should be a strong one. FT has been following the RGTA very precisely within the usual 10 to 14 day time lag. It reached a low point on Nov 24th/25th - 10 days after the RGTA did. FT has risen since then until Dec 1st, although it is still slightly -ve. It is now in the 10 to 14 day window when RGTA fell back sharply until Nov 30th/Dec 1st and FT should start falling again quite sharply from around Dec 2nd/3rd. Assuming RGTA is now on its next rising trend, then we can expect FT to rise again from around Dec 12th-15th and probably quite strongly. Now to the further 10 to 14 time lag between FT and global MT (GLMT). The peak in FT on Nov 10th was followed by a peak in GLMT on Nov 20th. The fall in FT from Nov 15th to its low point around Nov 25th is currently being matched with global MT still falling steadily and with the 10-14 lagged window it should reach its lowest point around Dec 5th-9th. Yesterday I said (wrt the Nov 30th chart) "it looks like GLMT will go -ve overall before rising again. Well the change to Dec 1st is quite dramatic with GLMT tumbling to its lowest level for many months (below the early Nov low point). Then GLMT should be rise again from around for about a week until Dec 12th-15th. Then it should see another big fall bottoming out around Dec 22nd-25th. Assuming that the rise in RGTA is now underway with FT rising from Dec 12th-15th, then we will see GLMT rising again around the Xmas period. it is this rise that may well be a strong and significant one - not the briefer rise just before mid December. Summary: I'll try to summarise what I said above with the low and high points for what we've seen recently and the expected changes for this month, assuming that RGTA rises strongly from now on and for a week or so. Please note that the time lagged responses are usually around 10 to 14 days and the predicted dates (shown in italics) may vary by 1 or 2 days earlier or later.. RGTA FT GLMT Low Point Nov 14th/15th Nov 24th/25th Dec 5th-9th High Point Nov 20th Dec 1st-2nd Dec 12th -15th Low Point Nov 30th/Dec 1st Dec 12th-15th Dec 22nd-25th High Point circa Dec 8th-12th circa Dec 18th-22nd circa Dec 28th-Jan 1st I am really sticking my neck out here but this should give an idea of what we might expect if everything falls into place. What we really need to look out for is how strong the changes and responses will be during this month's cycle. Remember it's not just the low and high points but the trends in the rises and falls. This is also highly simplified and the MJO, ENSO and other factors all come into play too. David
  3. Bring Back 1962-63

    Teleconnections: A More Technical Discussion

    Hi Tom, thank you for this very useful additional information. The 2008 paper that you refer to was one of the first that I placed into the Research Portal in early April. It is a superb read and written by Ed Berry and Dr Klaus Weickmann. It's essential for anyone learning about or increasing their AAM knowledge. I need to re-read some of these papers several times to get more of it to sink in and it really helps to return to it (or them) once one's knowledge of the basics has increased. Here's a direct link to the portal entry: The tropical Madden-Julian oscillation and the global wind oscillation with the abstract and link to the full paper. I copy the entry here: The tropical Madden-Julian oscillation and the global wind oscillation Authors: Klaus Weickmann and Edward Berry First Published: June 12th , 2008 Abstract: The global wind oscillation (GWO) is a subseasonal phenomenon encompassing the Madden-Julian Oscillation (MJO) and mid-latitude processes like meridional momentum transports and mountain torques. A phase space is defined for the GWO following the approach of Wheeler and Hendon (2004) for the MJO. In contrast to the oscillatory behavior of the MJO, two red noise processes define the GWO. The red noise spectra have variance at periods that bracket the 30-60 day band generally used to define the MJO. The MJO and GWO correlation accounts for 25% of their variance and crossspectra show well-defined phase relations. However, considerable independent variance still exists in the GWO. During MJO and GWO episodes, key events in the circulation and tropical convection derived from composites can be used for monitoring and for evaluating prediction model forecasts, especially for weeks 1-3. A case study during April-May 2007 focuses on the GWO and two ~30 day duration orbits with extreme anomalies in GWO phase space. The MJO phase space projections for the same time were partially driven by mountain torques and meridional transports. The case reveals the tropical-extratropical character of subseasonal events and its role in creating slowly evolving planetary-scale circulation and tropical convection anomalies Link to Paper: David
  4. Bring Back 1962-63

    Teleconnections: A More Technical Discussion

    Hi Tom @Isotherm and Zac @Snowy Hibbo, I wonder if some of the confusion is that there may still be some continuing technical issues with GFS AAM output. We also cannot get the GWO/FNL updates and the current charts have a 3 day time lag rather than 2 (that seems to happen sometimes over a weekend). We know that a few of the pros pay for the data and/or use their own data processing system but I wonder if others (other pros and many others) are struggling with the same technical issues that we have been? Ed Berry and Victor Gensini said several weeks ago that these issues are still being worked on and that GFS output charts were starting to re-populate - well there are still some strange inconsistencies with the forecast charts. Perhaps Anthony @antmasiello_HM would kindly come on here (we would all appreciate that ) and confirm what he was actually referring to with his statement about rising MT? After all, he said several months ago that he could not get the ex wdt output and was grateful to us for providing the links to Ed's friend's site. Taking all that into account, I'll post what I can with very brief comments below each chart: We know that the total GLAAM anomaly has been +ve for an extended period now for about 6 weeks. It climbed even higher during the second half of November and has only recently started to drift down slightly during the last week. The relative GLAAM tendency anomaly was +ve in early November, fell back towards mid-month (albeit remaining +ve) and rose slightly from Nov 15th-20th but has fallen steadily since then. In fact when it drops this low in fairly quick time, we know that a strong bounce back to +ve territory is highly likely quite soon to restore that imbalance. To me, the time lag for the FT response to the relative GLAAM tendency anomalies during recent weeks (since mid-November) is starting to get back on track. Isn't the lagged response much stronger in the winter season? The fall in the relative GLAAM tendency anomaly to its lowest (albeit still +ve) point in mid-Nov was followed 10 days later with FT at its lowest point (around Nov 24th/25th). The rel GLAAM tendency anom rise from Nov 15th-20th has been perfectly matched with FT rising from Nov 25th-30th. I think it was Tams @Tamara (but I may be misquoting her?) that explained to me that it wasn't the actual level of -ve or +ve response but the "trend response" that was most relevant - so although the rel GLAAM tendency anom remained +ve while FT was largely -ve, the actual changes in direction and the lagged responses from that point have been there since mid-Nov. With the rel GLAAM tendenncy anom falling steadily since Nov 20th, we should expect to see FT fall again during this week (10 to 14 days would be Nov 30th to Dec 3rd and the chart only shows up to Nov 30th). I would expect to see FT fall quite sharply later this week. The further 10 to 14 time lag between FT and MT is even clearer. The peak in FT on Nov 10th was followed by a peak in global MT on Nov 20th. The fall in FT from Nov 15th to its low point around Nov 25th is currently being matched with global MT still falling steadily and with the 10-14 lagged window it should reach its lowest point around Dec 5th-9th. It looks like it will go -ve overall before rising again. Then it should be rising for about a week but as FT is expected to fall sharply again this week, then global MT should fall sharply again around mid-Dec. Now if the big fall in the rel GLAAM tendency anom is followed by a big bounce back imminently, then FT should rise strongly after mid-month but the next "big" rise in global MT should not be until around or just after Xmas (with only that modest and brief rise around Dec 9th-15th). I won't go into the regional torques this time. Now the SCW GWO/FNL (final analysis) is stlll stuck on October 16th which is really annoying so we do not see the corrected or adjusted really accurate version. Let's look at the forecasts with extreme caution. Victor's bias corrected version is meant to adjust upwards the known -ve bias in the GEFS output and prior to the technical problems it was doing this - perhaps even slightly overcooked. Since the "re-population" the output seems to be somewhat (consistently) lower than it was. I wonder if either GFS did some work on correcting their own bias while dealing with their tech problems or whether Victor has made further adjustments to his bias correction version? I shall email Victor again about this and ask him for the very latest position on this during the week. The relative GLAAM anomaly is indeed close to the values shown on the most recent output but slightly above it. The low point is forecast to be this mid-week before a recovery but rel GLAAM anomaly is predicted to remain -ve throughout and trends lower after mid-month. We know that the CFS output has a continuous +ve bias perhaps by at least a factor of 1, possibly rather more. So just going by the forecast trend, rather than actual values, CFS expect the current fall to bottom out mid-week and then recover next week before trending down through to Xmas with hints of a recovery after that. I'll stick my fairly inexperienced neck out here and suggest that both the forecast charts look rather odd to me. Even if they have the general trend more or less right (which they may well not be) the fairly gentle changes are not very reflective of what we often see this time of year - stronger rises and stronger falls. The rest of you and particularly Tams @Tamara who have been studying this for much longer than myself might like to comment on all this. David
  5. Bring Back 1962-63

    Teleconnections: A More Technical Discussion

    Hi @Daimon, welcome to 33. We have loads of papers on SSWs in the Research Portal including the very recent one that you are looking for which introduces the new "DSW" classification: Sudden Stratospheric Warmings – developing a new classification based on vertical depth, applying theory to a SSW in 2018, and assessing predictability of a cold air outbreak following this SSW Just click on the title for a direct link to the portal entry and the abstract. From there you will find a direct link to the full paper that Malcolm @Blessed Weather placed in there on November 2nd. Check out the index while you are there for all the SSW and Stratosphere related papers: David
  6. Bring Back 1962-63

    Teleconnections: A More Technical Discussion

    Tom @Isotherm, Eric @Webberweather, Tams @Tamara and Zac @Snowy Hibbo. Like many others, I have been following this debate that, as @CCB! says, has "continued with scientific vigour". I am, however, somewhat concerned that the vigour and entrenched views proffered by Eric have gone rather too far and to say that Tom is completely wrong is both unhelpful and inaccurate. I did say several days ago that I hoped that the two of you could find the "common ground" that you "must" have despite your impasse on certain aspects of the AAM (atmospheric angular momentum) process. Even though I am still learning about all the AAM processes, I have gone beyond the basics and I have read many of the key papers on this subject. I am very grateful to Tams for assisting me through my learning process and patiently answering my questions during the last two years since I realised that I "must" endeavour to understand this vitally important teleconnection and how AAM interacts, influences and is influenced by other key teleconnections. Her post on here last week as I already said was outstanding and the best one so far on this entire thread and should be re-read by everyone as she went out of her way to explain the entire process (direct link): Now what I say may be a little muddled and I am entirely open to anyone correcting inaccuracies. The thrust of what Tams is saying is that you cannot look at ENSO in isolation. It is part of the GSDM (Global Synoptic Dynamic Model) and there are strong "cause and/or effect relationships or rather "golden rules" about how AAM and the torques, the ENSO state (and SSTs) and the MJO interact. At certain times one of these may play a major role and at others a minor role. There are seasonal differences too. Then using the brilliant GWO phase charts developed by Dr Klaus Weickmann and Edward K Berry (who also built the GSDM) we can see how what goes on in the tropics has direct influences on the sub tropics, the mid latitudes and polewards. I'll briefly go back to basics. The Rossby waves (aka planetary waves) that are generated through tropical convection have extraordinary atmospheric properties and influence the entire global circulation. Near the equator and in the tropics through lateral movement they control the equatorial jet, the WWBs (westerly wind bursts) and easterly trades and kelvin wave activity. Rossby waves propagate downwards and influence the upper sea surface layers and (what has only more recently been understood) deeper ocean currents. They influence the Walker circulation and cells and the thermocline. All this impacts on the ENSO state. The waves also propagate vertically and that is part of the MJO process. Then the most important property is that Rossby waves spread out polewards. This movement of air waves is always interacting with the rotation of the earth. This is what AAM is all about. It is permanently in a state of flux. As AAM moves across surfaces it can be slowed down by frictional interaction (Frictional Torque or FT). That creates an imbalance with faster and slower movements and the overall momentum (Total Global Angular Momentum or GLAAM) is always attempting to correct these imbalances and periods of -ve and +ve states will occur on varying time scales and to varying extents. Then we have the degree of relative GLAAM tendency compared to total GLAAM. When relative GLAAM tendency trends -ve or +ve there is a very reliable (almost fixed) time lagged response to the torques. Rising relative GLAAM will generate rising FT within 10 to 14 days. The poleward shift towards and throuigh the mid latitudes then interacts with the upper global westerlies (and the earth's rotation). These Rossby waves and rising AAM and then FT are also carried laterally. When they reach obstacles like the main mountain ranges, a further drag or torque is generated. This is MT (mountain torque). In this part of the relative GLAAM cycle, MT will rise about another 10 to 14 days following the rise in FT. This is all shown in the GWO charts and I repeat this below for learners: We have overall global MT and then regional MT which is generated by all the world's mountain ranges, including the tropics, Greenland and Antarctica but is much greater in the mid latitudes. The east Asian mountain massif (EAMT) and the N American Rockies (NAMT) generate about 85% of all MT between them. The Rossby waves and varying degrees of -ve and +ve MTs control the jet stream - it's strength, speed and particularly how it meanders and undulates around the globe. The largest mountain ranges can generate huge vertical uplifting properties. They can divert Rossby waves way up through the troposphere, into the stratosphere and even into the lower mesosphere. There has been a known link between this and warming events in the stratosphere. More recent studies and research have suggested that EAMT and a combination of the Himalayas, the Tibetan Plateau and the Mongolian Mountains may well be a key factor in triggering major SSW events. I've written several specialist posts on this (see the Tele thread index at the top of this page for links). Outside of the relative GLAAM tendency, FT and MT responses and the GWO phases, we also have FT and MT influences in the tropics themselves and their impact on total GLAAM. As Tams and Zac have shown in fairly recent updates, total GLAAM has trended very high recently while relative GLAAM tendency has been through strong +ve and -ve phases. Now this is where I feel there may have been a misunderstanding between Eric and Tom. I did mention this right at the start of their exchanges. Eric - you seem to be only referring to total GLAAM and your views seem to be based on AAM/ENSO responses in the tropics. Unfortunately, you do seem to be ignoring the much more significant relative GLAAM tendency and the golden rules of the whole GSDM process. I feel that you are talking cross purposes. With the greatest of respect to you and all your vastly superior ENSO knowledge, there is really no support for your views as you are missing the key relative AAM processes. I list these papers from the Research Portal which are about half of those under the AAM heading: Angular momentum in the global atmospheric circulation A Synoptic–Dynamic Model of Subseasonal Atmospheric Variability Atmospheric Dynamics Feedback: Concept, Simulations, and Climate Implications Atmospheric torques and Earth’s rotation: what drove the millisecond-level length-of-day response to the 2015–2016 El Niño? Axial Angular Momentum: Vertical Fluxes and Response to Torques Centennial Trend and Decadal-to-Interdecadal Variability of Atmospheric Angular Momentum in CMIP3 and CMIP5 Simulations Gravity wave refraction by three-dimensionally varying winds and the global transport of angular momentum Isentropic Pressure and Mountain Torques Latitude–Height Structure of the Atmospheric Angular Momentum Cycle Associated with the Madden–Julian Oscillation Mountains, the Global Frictional Torque, and the Circulation over the Pacific–North American Region Mountain torques and atmospheric oscillations Mountain Torques and Northern Hemisphere Low-Frequency Variability. Part I: Hemispheric Aspects Mountain Torques and Northern Hemisphere Low-Frequency Variability.Part II: Regional Aspects Regional Sources of Mountain Torque Variability and High-Frequency Fluctuations in Atmospheric Angular Momentum Stochastic and oscillatory forcing of global atmospheric angular momentum Studies of atmospheric angular momentum The Angular Momentum Budget of the Transformed Eulerian Mean Equations The atmospheric angular momentum cycle during the tropical Madden-Julian Oscillation The Dynamics of Intraseasonal Atmospheric Angular Momentum Oscillations The intraseasonal atmospheric angular momentum associated with MJO convective initiations Relationship between Tropical Pacific SST and global atmospheric angular momentum in coupled models The tropical Madden-Julian oscillation and the global wind oscillation Torques and the Related Meridional and Vertical Fluxes of Axial Angular Momentum Uncertainty analysis of atmospheric friction torque on the solid Earth Unusual Behavior in Atmospheric Angular Momentum during the 1965 and 1972 El Niños Where is ENSO stress balanced? I suggest that one reads the abstracts from those links above and then you can decide which papers you want to delve into more deeply. I usually speed read the introduction and the conclusions. Many of these papers explain the global atmospheric processes and the first 3 listed are as good as any in showing these. You'll see that Dr Klaus Weickmann crops up as the main or co-author in many of these papers. He was a pioneer (Carl Rossby wrote his initial paper on rossby waves back in 1939) in developing the understanding of AAM, FT. MT and along with Ed Berry devised the GSDM and the GWO. Out of almost every AAM paper that I've read, including some very recent ones since Klaus retired (in 2015) they all cite one or more of his papers. IMHO he is way out in front as the leader in the whole AAM field. I found this Klaus and Ed document in the NOAA maproom archives: The global AAM can only be changed by the action of global torques. However, we use the GWO as an index of zonal mean and regional changes in the circulation. This brings in other physical processes like momentum fluxes and Rossby wave dispersion. The global, zonal and regional relationships will be described in a paper in preparation. As an example, subseasonal zonal AAM changes are dominated by zonal mean momentum fluxes. As a result there is a difference between the latitude band where a torque generates an AAM anomaly, the band where the anomaly appears in the atmosphere and the latitude band where it is removed. The flux convergence of AAM is also the dominant forcing for the poleward movement of zonal AAM anomalies, which is a well-known MJO signal. Torques can be generated as a response to the meridional propagation of AAM anomalies. The poleward movement is produced by the phasing of fluxes due to the zonal mean mass circulations and those due to mid-latitude synoptic and other eddies. Wave breaking is a regional phenomenon that contributes to meridional movements in zonal mean AAM anomalies. It's part of the Berry/Weickmann NOAA document referencing the GSDM and GWO and here's the link: Last week, I also added Eric's cited paper that he referred to in one of his earlier posts: Response of the Zonal Mean Atmospheric Circulation to El Niño versus Global Warming Now all these papers, including this one, actually support Tom's view. This paper makes little or no reference to the AAM process, although the "Zonal Mean Atmospheric Circulation" is of course part of the wider global circulation that involves the GSDM processes. The paper is more slanted towards global warming and climate change. Whilst, undoubtedly there are impacts of global warming on many of the atmospheric process, there is no definitive research which proves that the higher SSTs are due to this either directly or indirectly. The decadal, centennial and longer term oscillations have been occurring for hundreds, if not, thousands of years and we must understand the degree of "natural variability" in conjunction with the anthropogenic influences. There are two important ENSO papers (not under the AAM heading) that are also highly relevant to this debate: A Review of ENSO Theories Global Warming and ENSO – A “Helter-Skelter” Atmosphere The first paper listed, published last month, goes back to those early El Nino events that both Eric and Tom refer to and goes right through to and beyond the 2015/16 event. It contains some fascinating points which have been so relevant to this year's events. The second paper discusses the 2015/16 event and global warming influences. I have many more papers and presentations in my store on AAM to add to the portal in the coming months. Overall, as I said, Eric and Tom have been talking cross purposes. Sometimes, when one states a view, one becomes more and more entrenched in that view and can dig oneself into a deeper hole. It is not really a question of being right or wrong but where one takes the starting point from. On this topic, it is misleading to oneself and the readers to take it from the ENSO perspective outwards. It is essential IMHO, to look at the much wider/global picture, the GSDM processes being a key part of that and seeing how ENSO fits into that process. I apologise if I have stopped sitting on the fence and appear to have taken sides in this debate. I never have any intention of upsetting anyone. As I said at the outset, I may have made a few errors myself but I believe that the basic thrust of what I say is correct and supported by all the papers that I've read and from my excellent tuition from @Tamara. Tams, I shall be delighted if you correct any part of this - it will benefit the learners as well as myself. David
  7. Observations of Coupling between Surface Wind Stress and Sea Surface Temperature in the Eastern Tropical Pacific Authors: Dudley B. Chelton, Steven K. Esbensen, Michael G. Schlax, Nicolai Thum and Michael H. Freilich First Published: December 27th, 1999 Published on line: April 1st, 2001 Abstract: Satellite measurements of surface wind stress from the QuikSCAT scatterometer and sea surface temperature (SST) from the Tropical Rainfall Measuring Mission Microwave Imager are analyzed for the three-month period 21 July–20 October 1999 to investigate ocean–atmosphere coupling in the eastern tropical Pacific. Oceanic tropical instability waves (TIWs) with periods of 20–40 days and wavelengths of 1000–2000 km perturb the SST fronts that bracket both sides of the equatorial cold tongue, which is centered near 1°S to the east of 130°W. These perturbations are characterized by cusp-shaped features that propagate systematically westward on both sides of the equator. The space–time structures of these SST perturbations are reproduced with remarkable detail in the surface wind stress field. The wind stress divergence is shown to be linearly related to the downwind component of the SST gradient with a response on the south side of the cold tongue that is about twice that on the north side. The wind stress curl is linearly related to the crosswind component of the SST gradient with a response that is approximately half that of the wind stress divergence response to the downwind SST gradient. The perturbed SST and wind stress fields propagate synchronously westward with the TIWs. This close coupling between SST and wind stress supports the Wallace et al. hypothesis that surface winds vary in response to SST modification of atmospheric boundary layer stability. Link to full paper:<1479%3AOOCBSW>2.0.CO%3B2
  8. Narrowing of the ITCZ in a warming climate: Physical mechanisms First published: 22 October 2016 Authors: Michael P. Byrne and Tapio Schneider First Published: October 22nd, 2016 Published on line: June 14th, 2016 Abstract: The Intertropical Convergence Zone (ITCZ) narrows in response to global warming in both observations and climate models. However, a physical understanding of this narrowing is lacking. Here we show that the narrowing of the ITCZ in simulations of future climate is related to changes in the moist static energy (MSE) budget. MSE advection by the mean circulation and MSE divergence by transient eddies tend to narrow the ITCZ, while changes in net energy input to the atmosphere and the gross moist stability tend to widen the ITCZ. The narrowing tendency arises because the meridional MSE gradient strengthens with warming, whereas the largest widening tendency is due to increasing shortwave heating of the atmosphere. The magnitude of the ITCZ narrowing depends strongly on the gross moist stability and clouds, emphasizing the need to better understand these fundamental processes in the tropical atmosphere. Link to Paper:
  9. Energetic Constraints on the Width of the Intertropical Convergence Zone Authors: Michael P. Byrne and Tapio Schneider First Published: February 9th, 2016 Published on line: June 14th, 2016 Abstract: The intertropical convergence zone (ITCZ) has been the focus of considerable research in recent years, with much of this work concerned with how the latitude of maximum tropical precipitation responds to natural climate variability and to radiative forcing. The width of the ITCZ, however, has received little attention despite its importance for regional climate and for understanding the general circulation of the atmosphere. This paper investigates the ITCZ width in simulations with an idealized general circulation model over a wide range of climates. The ITCZ, defined as the tropical region where there is time-mean ascent, displays rich behavior as the climate varies, widening with warming in cool climates, narrowing in temperate climates, and maintaining a relatively constant width in hot climates. The mass and energy budgets of the Hadley circulation are used to derive expressions for the area of the ITCZ relative to the area of the neighboring descent region, and for the sensitivity of the ITCZ area to changes in climate. The ITCZ width depends primarily on four quantities: the net energy input to the tropical atmosphere, the advection of moist static energy by the Hadley circulation, the transport of moist static energy by transient eddies, and the gross moist stability. Different processes are important for the ITCZ width in different climates, with changes in gross moist stability generally having a weak influence relative to the other processes. The results are likely to be useful for analyzing the ITCZ width in complex climate models and for understanding past and future climate change in the tropics. Link to Paper:
  10. Atmospheric Dynamics Feedback: Concept, Simulations, and Climate Implications Authors: Michael P. Byrne and Tapio Schneider First Published: January 12th, 2018 Published on line: March 26th, 2018 Abstract: The regional climate response to radiative forcing is largely controlled by changes in the atmospheric circulation. It has been suggested that global climate sensitivity also depends on the circulation response, an effect called the “atmospheric dynamics feedback.” Using a technique to isolate the influence of changes in atmospheric circulation on top-of-the-atmosphere radiation, the authors calculate the atmospheric dynamics feedback in coupled climate models. Large-scale circulation changes contribute substantially to all-sky and cloud feedbacks in the tropics but are relatively less important at higher latitudes. Globally averaged, the atmospheric dynamics feedback is positive and amplifies the near-surface temperature response to climate change by an average of 8% in simulations with coupled models. A constraint related to the atmospheric mass budget results in the dynamics feedback being small on large scales relative to feedbacks associated with thermodynamic processes. Idealized-forcing simulations suggest that circulation changes at high latitudes are potentially more effective at influencing global temperature than circulation changes at low latitudes, and the implications for past and future climate change are discussed. Link to Paper:
  11. Fast and Slow Components of the Extratropical Atmospheric Circulation Response to CO2 Forcing Authors: Paulo Ceppi, Giuseppe Zappa, Theodore G. Shepherd and Jonathan M. Gregory First Published: September 15th, 2017 Published on line: January 19th, 2018 Abstract: Poleward shifts of the extratropical atmospheric circulation are a common response to CO2 forcing in global climate models (GCMs), but little is known about the time dependence of this response. Here it is shown that in coupled climate models, the long-term evolution of sea surface temperatures (SSTs) induces two distinct time scales of circulation response to steplike CO2 forcing. In most GCMs from phase 5 of the Coupled Model Intercomparison Project as well as in the multimodel mean, all of the poleward shift of the midlatitude jets and Hadley cell edge occurs in a fast response within 5–10 years of the forcing, during which less than half of the expected equilibrium warming is realized. Compared with this fast response, the slow response over subsequent decades to centuries features stronger polar amplification (especially in the Antarctic), enhanced warming in the Southern Ocean, an El Niño–like pattern of tropical Pacific warming, and weaker land–sea contrast. Atmosphere-only GCM experiments demonstrate that the SST evolution drives the difference between the fast and slow circulation responses, although the direct radiative effect of CO2 also contributes to the fast response. It is further shown that the fast and slow responses determine the long-term evolution of the circulation response to warming in the representative concentration pathway 4.5 (RCP4.5) scenario. The results imply that shifts in midlatitude circulation generally scale with the radiative forcing, rather than with global-mean temperature change. A corollary is that time slices taken from a transient simulation at a given level of warming will considerably overestimate the extratropical circulation response in a stabilized climate. Link to Paper:
  12. Response of the Zonal Mean Atmospheric Circulation to El Niño versus Global Warming Authors: Jian Lu, Gang Chen and Dargan M. W. Frierson First Published: March 11th, 2008 Published on line: November 15th, 2008 Abstract: The change in the zonal mean atmospheric circulation under global warming is studied in comparison with the response to El Niño forcing, by examining the model simulations conducted for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. In contrast to the strengthening and contraction of the Hadley cell and the equatorward shift of the tropospheric zonal jets in response to El Niño, the Hadley cell weakens and expands poleward, and the jets move poleward in a warmed climate, despite the projected “El Niño–like” enhanced warming over the equatorial central and eastern Pacific. The hydrological impacts of global warming also exhibit distinct patterns over the subtropics and midlatitudes in comparison to the El Niño. Two feasible mechanisms are proposed for the zonal mean circulation response to global warming: 1) The increase in static stability of the subtropical and midlatitude troposphere, a robust result of the quasi-moist adiabatic adjustment to the surface warming, may stabilize the baroclinic eddy growth on the equatorward side of the storm tracks and push the eddy activity and the associated eddy-driven wind and subsidence poleward, leading to the poleward expansion of the Hadley cell and the shift of midlatitude jets; 2) the strengthening of the midlatitude wind at the upper troposphere and lower stratosphere, arguably a consequence of increases in the meridional temperature gradient near the tropopause level due to the tropospheric warming and tropopause slope, may increase the eastward propagation of the eddies emanating from the midlatitudes, and thus the subtropical region of wave breaking displaces poleward together with the eddy-driven circulation. Both mechanisms are somewhat, if not completely, distinct from those in response to the El Niño condition. Link to full paper: Credit goes to Eric @Webberweather for finding this presentation - thank you.
  13. Bring Back 1962-63

    Teleconnections: A More Technical Discussion

    Some absolutely brilliant posts today on here. Thank you Tams @Tamara, your latest post is outstanding and should be on the short list for "post of year" - so well described and explained and 33 is so lucky to have your contributions. I'll need to re-read it a few times to digest it all. Then Tom @Isotherm and Eric @Webberweather what a discussion You both argue your points so well and it would be very easy to be convinced by either view! All I can do is say that I've read many papers on AAM and how it interacts and influences (or is influenced by) other key teleconnections and my mind is often "boggled" trying to understand the more technical parts. Some of these papers are by highly specialist authors on this topic and I can see that there are some conflicting views between them. I'm sure that the two of you have some common ground as well as your differences of opinion. Remember that there are a number of readers following all of this on here, so it would be useful that both of you explain your points clearly for our benefit. This is exactly the type of debate that should be thoroughly encouraged. So thank you to both of you. You have both cited some papers. I have or will continue to place these in the Research Portal and give you the appropriate credit for them. There are also a few papers already in the portal which may support either of your stated views. I have also added a more recent one from the same author that Tom cited. I'll check my huge store of papers and presentations again right now (at least another 50+ on AAM to add in due course) to see if there are others which are highly relevant right now - if so, I'll add these today. David
  14. Relationship between Tropical Pacific SST and global atmospheric angular momentum in coupled models Authors: Huei−Ping Huang, Matthew Newman, Richard Seager, Yochanan Kushnir and Participating CMIP2+ Modeling Groups First Published: January 2004 Abstract: The sensitivity parameter S1 = ∆AAM/∆SST, where ∆AAM and ∆SST represent the anomalies of global atmospheric angular momentum (AAM) and tropical Pacific sea surface temperature (SST) in the NINO3.4 region, is compared for the CMIP2+ coupled models. The parameter quantifies the strength of atmospheric zonal mean zonal wind response to SST anomaly in the equatorial Pacific, an important process for the climate system. Although the simulated ∆AAM and ∆SST are found to exhibit great disparity, their ratios agree better among the coupled models (and with observation) with no significant outliers. This indicates that the processes that connect the AAM anomaly to tropical SST anomaly are not sensitive to the base SST and the detail of convective heating and are relatively easy to reproduce by the coupled models. Through this robust ∆SST−∆AAM relationship, the model bias in tropical Pacific SST manifests itself in the bias in atmospheric angular momentum. The value of S1 for an atmospheric model forced by observed SST is close to that for a coupled model with a similar atmospheric component, suggesting that the ∆SST− ∆AAM relationship is dominated by a one−way influence of the former forcing the latter. The physical basis for the ∆SST−∆AAM relationship is explored using a statistical equilibrium argument that links ∆SST to the anomaly of tropical tropospheric temperature. The resulting meridional gradient of tropospheric temperature is then linked to the change in zonal wind in the subtropical jets, the main contributor to ∆AAM, by thermal wind balance. Link to Paper: Credit goes to Tom @Isotherm for finding this paper - thank you.
  15. Centennial Trend and Decadal-to-Interdecadal Variability of Atmospheric Angular Momentum in CMIP3 and CMIP5 Simulations Authors: Houk Paek and Huei-Ping Huang First Published: 26th November, 2012 Published on line: 31st May, 2013 Abstract: The climatology and trend of atmospheric angular momentum from the phase 3 and the phase 5 Climate Model Intercomparison Project (CMIP3 and CMIP5, respectively) simulations are diagnosed and validated with the Twentieth Century Reanalysis (20CR). It is found that CMIP5 models produced a significantly smaller bias in the twentieth-century climatology of the relative MR and omega MΩ angular momentum compared to CMIP3. The CMIP5 models also produced a narrower ensemble spread of the climatology and trend of MR and MΩ. Both CMIP3 and CMIP5 simulations consistently produced a positive trend in MR and MΩ for the twentieth and twenty-first centuries. The trend for the twenty-first century is much greater, reflecting the role of greenhouse gas (GHG) forcing in inducing the trend. The simulated increase in MR for the twentieth century is consistent with reanalysis. Both CMIP3 and CMIP5 models produced a wide range of magnitudes of decadal and interdecadal variability of MRcompared to 20CR. The ratio of the simulated standard deviation of decadal or interdecadal variability to its observed counterpart ranges from 0.5 to over 2.0 for individual models. Nevertheless, the bias is largely random and ensemble averaging brings the ratio to within 18% of the reanalysis for decadal and interdecadal variability for both CMIP3 and CMIP5. The twenty-first-century simulations from both CMIP3 and CMIP5 produced only a small trend in the amplitude of decadal or interdecadal variability, which is not statistically significant. Thus, while GHG forcing induces a significant increase in the climatological mean of angular momentum, it does not significantly affect its decadal-to-interdecadal variability in the twenty-first century. Link to Paper: